The happiest day for me before I got married was when I graduated from university. That day I felt like I was over the moon!! :)
Then my wedding day was the happiest day. But since I had two little kids. When I had them was the happiest day. So it keeps changing. But I think to date, having them was the best experience of my life!!
The saddest day - When I was barely 7 years old, my brother who was 3 and a half years old at the time, died of measles related complications. To this day, that day haunts me. That was the worst day of my life and the worst day of my family's life too. Every year on his death anniversary, I feel awful. Even after so many years, I miss him. So that is the worst day of my life.